Project Abstract The broad, long-term objective of this project is to evaluate the therapeutic value of vein of Marshall (VOM) ethanol infusion when added to catheter ablation of atrial fibrillation (AF). AF is the most common sustained arrhythmia in adults, and it is a leading cause of stroke, disability and increased mortality. Catheter ablatin - pulmonary vein (PV) antral isolation (PVAI)- can lead to cure, but is best suited for paroxysmal AF, in which ectopic beats arising from the pulmonary veins were shown to initiate AF. PVAI success is lower in persistent AF, in which the role of the cardiac autonomic system, particularly the intrinsic cardiac ganglia, is being increasingly recognized. Expanding the ablation lesions to include greater areas the left atrial (LA) anatomy marginally improves outcomes, but also leads to increases in procedural complexity and duration, need of repeat procedures, and complications such as atrial flutters, particularly perimitral flutter (PMF). We have developed a technique to perform rapid ablation of atrial tissues in AF using ethanol infusion in the vein of Marshall (VOM), and have shown: 1) Effective, rapid and safe tissue ablation of LA tissue neighboring the LA ridge and left inferior PV; 2) Regional LA vagal denervation by reaching the intrinsic cardiac ganglia; and 3) Facilitation of cure of PMF by ablating most of the mitral isthmus. We propose to evaluate outcomes differences yielded by VOM ethanol when added to conventional PVAI. The specific aims are: #1.To assess the impact of VOM ethanol infusion in procedure success when added to de novo catheter ablation of persistent AF. We will randomize patients with persistent AF undergoing a first AF ablation to standard PVAI vs a combined VOM ethanol infusion plus PVAI (VOM-PV). #2. To assess the impact of VOM ethanol infusion added to repeat catheter ablation of recurrent AF after a failed ablation. Patients undergoing a repeat procedure for persistent AF after a failed PVAI will be randomized to either PVAI or VOM-PV as their repeat procedure. End points will include freedom from symptomatic or electrocardiographic AF after 12-15 months.